The present invention is directed to an apparatus for positioning the head of a patient for producing an x-ray picture, particularly a dental panoramic tomogram, by means of which the head of the patient is positionable so that it assumes a defined position relative to a fixed point with respect to at least one projection plane and this fixed point, in turn, assumes a defined position relative to a central ray proceeding between an x-ray tube serving the purpose of producing an x-ray picture in an x-ray radiation receiver lying opposite to the x-ray tube.
A dental x-ray diagnostics installation comprising an x-ray source, an x-radiation receiver and means for positioning the head of a patient between the two is described in a Siemens Company sales brochure entitled "Minimize X-ray Dosage, Maximize Image Quality . . . ", Order No. A19100-M47-A361-01-766. The known apparatus comprises a light source, by means of which a stroke-shaped light marks are cast onto the head of a patient. These light marks comprise a defined position and define a course both relative to a fixed point, as well as relative to a projection plane belonging to the respective light mark. The head of the patient is positioned so that the stroke-shaped light marks coincide with pronounced lines at the head of the patient, for example, the Frankfurt Horizontals. The head of the patient then assumes the defined position relative to the fixed point required for the production of the picture and is held in this position by a head support. The positioning of the head of the patient with the known apparatus is an involved nature and is time-consuming. Moreover, the attending person must be present at the x-ray diagnostics installation during the step of positioning the head of the patient and they must then proceed behind the protective wall while producing or taking the x-ray picture.
In U.S. Pat. No. 3,708,663, whose disclosure is incorporated by reference, a similar positioning means is described for a cephalostat and the apparatus with which a skull picture of a patient can be produced. In order to be able to position the head of the patient in the three degrees of freedom (x, y, and z), a light beam projector, which generates both horizontal and vertical light rays, is provided. The light beam projector is arranged relative to the x-radiation source with the horizontal light ray and the central ray of the x-ray source lying in the same horizontal plane. A mirror, that reflects the vertical and horizontal light rays of the light beam projector, is positioned at a distance from the patient's head at an angle relative to the light rays of the projector and also at an angle relative to the vertical plane, which proceeds through the center of the patient's head. With the assistance of the reflected light rays and of the light rays directly cast onto the patient's head, the patient's head can be adjusted with respect to the Frankfurt Horizontal and with respect to the sagittal plane. Apart from the fact that the mirror being positioned immediately in front of the patient's head is disturbing, the alignment of the patient by visual comparison of the light rays directly cast onto the patient with the light rays reflected via the mirror, which are the indirect incident light rays, is comparatively involved and not precise.
U.S. Pat. No. 4,262,306, whose disclosure is incorporated by reference thereto, discloses an apparatus for supervision of the positioning of a patient or a region of a patient, which serves the purpose for repeat treatments of being able to bring the body or body part, respectively, of the patient into an optimally precise position, which coincides with the original position. To this end, a camera arranged spatially-rigid and/or source-rigid is provided. This camera is directed onto the patient and/or onto the radiation source. Picture elements of the first positional image are deposited in a storage by a camera. Comparison means are provided, first, with the picture element data of the first stored positional image and, secondly, with the second, current positional image produced during a repeated treatment and are subsequently converted so that the picture elements of both positions appear on an image carrier. On the basis of a correction of the position of the patient, the second and current positional image can be adapted and brought into coincidence with the previous image position. The storing of the first position can occur in a photographic way on the basis of an x-ray picture or on the basis of electromagnetic memories. The comparison means can comprise an inverter and an addition circuit or can also comprise a subtraction circuit, with which the individual picture elements can be directly compared to one another and can be represented superimposed on one another. However, this patent does not teach how the patient's head can be exactly positioned for a panoramic tomogram, namely, during the initial exposure. The positioning for the initial exposure in this known apparatus continues to occur "manually" based on the feeling of the operational personnel. It is only repeat pictures, which can be reproduceably produced in this known apparatus, in accordance with the position during the first exposure. However, if, during the initial exposure, the exact position was not obtained, then subsequent exposures will also be out of position. Since an exact positionig of a patient's head is indispensible, particularly when producing tomograms of the jaw region of the patient, a device which provides exact initial positions and subsequent positions is desired.